Antenna system



June 6, l950 DE wrrr R. GODDARD 2,510,20

ANTENNA SYSTEM y Filed Sept. 10, 1946 /a \/L// YM /4' f ZZ Y f4 IN VEN TOR.

Patented June 6, 1950 UNITED of Delaware Application September 10, 194.6, Serial No. 695,893

4 Claims.

vThis invention relates to radio communication systems and more particularly to an improved multiple unit steerable antenna system.

It is well known in the art that two or more antenna units, such as vertical antenna elements, may be so spaced in a radio system and their currents so related in phase as to produce a fairly sharp receiving directive characteristic or diagram. It is also known that the characteristic may be shifted by varying the phase relation of the currents. Such shifting is known as steering the antenna array.

In order to achieve a satisfactory steerable unit, it is known to select directive antenna units, such as rhombic units, each having a relatively sharp lobe. The resultant lobe for the combination is equal to the product along any wave direction or axis of the effective unit lobe and the array lobe and is exceedingly sharp.

By adjusting the phase shifts, the position of the resultant lobe may be varied to select one wave direction while excluding all others and thereby enable the operator to select the most favorable angle for eicient operation under adverse conditions. As is known, the most eilicient angle of reception varies according to the time of day, position of the I-Ieaviside layer, atmosphere conditions and the like.

In order to obtain satisfactory selectivity, multiple unit steerable antenna systems in use today require a plurality of antennas covering several miles. At present a multiple unit steerable antenna system may use perhaps six antennas spaced so as to cover perhaps three miles. Such a system requires elaborate and costly apparatus, a large portion of which is represented in the equipment needed to feed the signal from the antennas to the place at which they are utilized. It is desirable to utilize a practical and relatively inexpensive antenna array for the purpose of obtaining an easily controllable directive characteristic which is sharp enough to eiect improved communication and eliminate fading.

According to the present invention a system is provided that will require a much less extensive array of antennas than is required by present day systems. By means of the invention, instead of spacing the antennas so as to cover three miles as in the example cited above, it will be possible to space a corresponding number of antennas over three-tenths of a mile and yet lhave the same degree of angular resolution.

Accordingly, it is a prime object of this invention to provide an improved multiple unit steerable antenna system which will allow closer spacling between antenna units of an array without loss of angular resolution.

Briey, in accordance with the invention, the incoming wave received and detected from each antenna is heterodyned with a common oscillator to produce output currents of equal frequency, the output currents being used to drive harmonic generators which multiply the phase difference of the incoming signal as it appears from the various antennas and the signals then translated as is customary.

The above and other objects and advantages will become apparent upon a consideration of the following detailed description when taken in connection with the accompanying drawing in which an embodiment of the invention is illustrated in block diagram.

In the drawing, I0, Il, I2, I3, I4 and I5 represent a plurality of antenna units of a multiple unit steerable antenna system, six in the example illustrated. These antenna units may well be of the rhombic type although almost any type of antenna unit may be used. In order to increase further the selectivity, particularly in point-to-point communication, these antenna units will normally be located in a line directed toward the source of the signal. Transmission lines 2Q, 2l, 22, 23, 24 and 25 direct the signal from the antennas I0 to I5 to a corresponding number of mixers represented in the drawing by block 30. In order'to prevent an undesired phase shift due to the difference in the physical length of the electrical paths between the antenna units and the mixers, the transmission lines are designed to have the same eifective electrical length. Such lines are of known construction and will not be further described.

In a preferred form of the invention the mixers 30 are excited by a common oscillator 32 to produce, by Way of example, an intermediate frequency of say kilocycles. It will be apparent that any convenient intermediate frequency may be chosen. It will also be obvious that separate oscillators, kept in phase, may be used with each mixer so long as the output currents have equal intermediate frequencies. However, in the interest of avoiding unnecessary duplication of apparatus, a common oscillator is preferred.

The outputs of mixers 30 feed a corresponding number of intermediate frequency amplifiers 34 tuned to the 'output frequency of the mixers. These ampliers in turn drive a corresponding number of harmonic generators 36. These harmonic generators are arranged to multiply the frequency of the output currents of mixers 30. For purposes of illustration it will be'assumed that the intermediate frequencies are multiplied by ten, producing (in the example chosen) frequencies of 1000 kilocycles.

The harmonic generators 36 when used for telegraphy and other similar methods of modulation may conform to any' Well'known system. However, in the case of voiceor sound amplitude modulation, the` harmonic generator must be of a special nature. That is, it must produce habmonics of carrier or intermediate frequency components Without limiting olfY amplitude variations. A harmonic generator suitable for this purpose is described in my copendingapplication Serial No. 580,211, filed February 28, 1945, now

Patent No. 2,468,624, granted April 26, 1949..V Phase and frequency modulation do not require.

this special type of harmonic generator.

The outputs of the harmonic generators 36 pass through individual 1000 kilocycle band pass filters 38 into separate 1000 kilocycle intermediate frequency amplifiers 40. Such band pass filters and intermediate frequency amplifiers may be of any known design Which will perform the desired operations.

The 1000 kilocycle amplifiers 40 in turn feed a corresponding number of phase changers 42. These phase changers are provided in order to secure a maximum eifect at the receiver for a given incoming direction, and to render the out-ofphase components absorbed by the antenna units in phase at the receiver. The arrangement is such that the various antenna )units deliver to the receiver an in-phase resultant of the incoming signal at which the maximum lobe of the array is steered.

The outputs of phase changers 42 are combined and demodulated in asingle detector 44 which feeds an indicating device 46 or other means of translating the signal.

In describing the operation of the invention, it Will be assumed that the antenna units are spaced to cover three-tenths of Ya mile as opposed to other systems in which a comparable antenna array would have to be spaced so as to cover three miles. An incoming signal Will produce in each antenna Y unit signal components similar but differing in phase. The signal components will be heterodyned in mixers 30 with the oscillations produced by oscillator 32. The outputs of mixers 30 then pass to intermediate amplifiers 34. Changes Vin relative phase of the incoming signal components from the various antennaswill, accordingly, produce identical changes in phase in the 100 kilocycle amplifiers 34. These changes'in phase will be about one-tenth as large as Vthey would be Were the antennas spaced so as to cover three miles and therefore the system would appear .to be insensitive. Y

However, the outputs of intermediate frequency amplifiers 34 drive the harmonic generator 3S Where the frequency is multiplied by say ten, to produce 1000 kilocycle signals. At the same time there results a multiplication of the phase differences by the same factor, in the present example by ten. The result is to present to the phase `changers 42 phase differences which correspond to those which would be produced by a system having an antenna array spaced over an area ten times as great but not using the invention. By means Vof this arrangement, the phase sensitivity of the closely spaced antenna array will be brought up to equal that of a greater spaced antenna array. The outputs of the phase changers are then combined in a common detector 44 and translated as desired.

What is claimed is:

1. In combination, a plurality of antenna units. separate mixers connected to each of said antenna units, said mixers having terminals adapted to receive oscillations to produce signals having equal intermediate frequencies representative of intelligence, separate harmonic generators driven by said signals connected to each of said mixers,

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said harmonic generators being arranged to multiply equally the frequency of said signals, separate phase changers connected to each of said harmonic generators to receive the output thereof, a single detector connected to said phase changers arranged to demodulate the output from said phase changers, and a translating device connected to said single detector.

2. In a radio communicating system, a plurality of antenna units, separate mixers connected to `each of said Vantenna units, said mixers having terminals adapted to receive oscillations to produce signals having equal intermediate frequencies representative of intelligence but differing in phase, separate harmonic generators driven by said signals connected to each of said mixers, said harmonic generators being arranged to multiply equally the phase difference of said signals, separate phase changers connected to each of said harmonic generators to receive the output thereof, a single detectorV connected to said phase changers arranged to demodulatethe output from said phase changers, and a translating device connected to said single detector.

3. A radio communication system comprising-a plurality of antenna units, separate channels for each of said 'antenna units, separate mixers in each of said lchannels, said mixers having terminals adapted -to receive oscillations to produce signals of equal frequency'representative of intelligence in each of said channels, separate phase Y changers in each of 'said channels, separatehar- Vmonic generators in Veach of said channels connected between said phase changers` and said inixers,1said harmonic generators being driven by said signals and arranged to multiply equally the lfrequency of said signals, a single detector lconnected to said rphase changers arranged to demodulate the outputY from said phase changers and a ,to saidV single channels, separate harmonic generators 'in each i of said channels connected between said phase changers and said mixers, said harmonic generators being drivenv by said signals and arranged to multiply equally the phase difference of said signals, a single detector connected to said phase changers arranged VVto demodulate the output from said phase changers and a translating de-V vice connectedto said single detector.

DE WI'IT R. GODDARD.

CITED The following references are of record inthe iile of this patent:

UNLIED STATES PATENTS Koechlin July 1, 1947 

